The aim of this research is to estimate the magnitude of school segregation by socioeconomic level in Spain and Autonomous Communities, comparing the results with the countries of the European Union. For this purpose, it performs a special exploitation of the PISA-2015dataset, using the Gorard and Isolation indices. The results indicate that the average segregation is Spain in its unevenness dimension is 0.38 (Gorard index) and 0.32 in its exposure dimension (Isolation index). These findings indicate that Spain is one of the most segregated countries in Europe, similar to those countries in the East that are more segregated and far from the countries in their closest context. School segregation in the Autonomous Communities offers extreme results, some of which are among the lowest in Europe (Illes Balears, Galicia and Aragon) and others such as the Community of Madrid with a very high segregation, only surpassed by Hungary within the European Union. Our findings highlight the impact of regional educational policies on the admission criteria to schools into school segregation, showing that policies such as the promotion of private education, the competence of schools through the publication of rankings or the creation of a single district can set up unequal educational systems that attempts equal opportunities.